Ground detecting apparatus



United States Patent Ofilice 2,697,217

Patented Dec. 14, 1954 1 2 41 and a make contact 42, which contacts arerespec? tively cooperable with fixed contacts 44, 45, 46.

2,697,217 As may be seen from the drawing, the contacts 28,

41, are connected together by a wire 50 and the con- GROUND DETECTINGAPPARATUS 5 tacts 30, 42, are connected together by a wire 51. The

. front contacts 32, 34 and 45 of the relays are connected ifi a fi g 53232? g' 'z z g' gg g' sg gzs; to the neutral or center wire 13, as byleads 52, 5 4, 55, York P y t a respectively, and a signal indicatordesignated 57, such Application March 17, 1953, serial No. 342,900 Theiixed back contacts 31, 44, are connected together 1 Clai (Cl, 340 255)the front contact 46 engaged by the make contact 42 Since the rectifiers20, 21 are connected across wires This invention relates to apparatusfor detecting the in pp relation to h other as Shown, no presence of aground on three-wire alternating current current of practical magnitudeflows through the rectielectrical systems, all of the conductors ofwhich are hers or relay coils 24, 37, because one of the rectifiers ityin detecting and indicating the presence of a ground Cycle 111 addition,When Wires 13 and 14 are connection with any one of the three wires in asystem lated from g there is I10 Substantial return P supplying power toa hazardous location. For example, m either Of the grounded relay coilsto any of the in a hospital operating room there exists the serious r ThC rr n in the reetifiers and relay Coils is,

hazard or ignition of explosive anesthetic gases or vapors therefore,normally y Close t0 ZetO- Under these by electrical sparks. To mi imithi ha rd, s b nconditions, the coils are not energized and the signaltially every object in an operating room is electrically indieaters 57are all 011 p ciretlitshowever, one grounded, including the patient,furniture and apparatus, f h Wires, as for example Wife 12, becomes insome and including the personnel in attendance, through conway connectedto ground, current will flow during the ductive shoes d flo i positivehalf cycle from wire 14 through rectifier 21,

Since the patient and attending personnel are grounded, cell 37 toground, and thence through the faulty cot! the power supply system mustb i ol ted f o ground nection back to wire 12. In other words, relaywill y means of an isolatinng transformer to prevent the be pp Wlth apulsating direct Current having 3 P personnel to be warned immediatelyif there is any con- 3 44 and into engagement with front contact 45 andcausand ground. tact 46 Relay 22 will remain deenergtzed since theAccordingly, it is a primary object of this invention circuit isgrounded at both ends. The closing of conto provide an apparatus,embodying a ini m f equiptacts 41, 45, completes a circuit from wire 13through ment and functioning with a small current flow, which e Signalindicator 57 (numbered Contacts will give a visible or audible signalupon the occurrence Wire Contacts Wire 58, Wife 60 to of a ground on anyof the wire of the i olated power wire 12. Thus the signal 57 (numbered12) receives system. a potential equal to the potential between thewires 12,

A more specific object of the invention is to provide 13. Since therelay 22 is not energized, the circuits of an apparatus which willindicate which wire of a three- 4 the other two signal indicators 57remain open and only wire system is connected to ground. the indicator57 (numbered 12) is actuated, indicating Other objects and advantages ofthe invention will that wire 12 has a ground fault. The indicators 57become apparent from a reading of the following demay, of course, beC0101 coded, tagged or otherwise suittailed description together withthe accompanying drawably designat d t indicate WhiCh Wife has theground ing, and from the appended claims. 50 fault when one of theindicators is actuated.

The drawing is a schematic wiring diagram illustrating If wire 14 is thegrounded wire, the operation of an electrical circuit and arrangementpfapparatus therein the apparatus is similar to the operation justdescribed on any of the three wires of an alternating currentelecdeetlelgized- In etlch Case, y the Signal lndlcatol' 57 tricalystem, (numbered 14) 1S actuated to show that wire 14 has In thedrawing, which illustrates a typical embodiment h g n f l a circuit eingmpleted from wire of the invention for the purposes of detaileddisclosure, 13 through the indicator, Contacts lead 12, 13 and 14designate the wires of the three-wire power taets 44 and leads back toWife 2- supply system extending from the secondary winding 15 in theevent that center wire 13 is the wire connected of an isolatingtransformer having a primary winding 60 to ground, both relays areenergized in the manner de- 16 connected to supply line 17, 18. In thissystem, wire scribed hercinabove. Since contacts 31, 28 and 41, 44 13serves as the neutral, and in ordinary practice the are open, signalindicators 57 (numbered 12 and 14) potential between wire 13 and eitherof the wires 12, 14 are in open circuits and are not actuated; however,the is 115 volts, while the potential across wires 12, 14 is indicator57 (numbered 13) is actuated to indicate that 230 volts. wire 13 has theground fault. In this case, the circuit A pair ofunidirectionally-conductive devices, such as is completed from Wire 12through leads 60, 61, conrectifier-s 20, 21, are connected to outsidewires 12 14, tacts 42, 46, le d 5 C nta ts 30, 34, lead 54 and therespectively. These devices permit current flow thereindicator to wire13, through in the direction of the arrowheads only. The What I claimis: rectifier 20 is connected to the energizing circuit of a Grounddetecting apparatus for a three-wire alternat relay 22 having a coil 24grounded at 25. Relay 22 ing current system wherein the conductors areisolated is adapted to actuate a transfer contact 28 and a make fromground, a pair of unidirectionally-conductive decontact 30. The transfercontact 28 normally engages vices respectively connected to oppositeoutside wires a fixed back contact 31 when the relay is deenergized ofsaid system, a pair of relay elements each having and this transfercontact 28 moves into engagement with an energizing circuit respectivelyconnected to said dea fixed front contact 32. When the relay becomesenervices, the opposite sides of said relays being connected gized, themake contact 30 moves into engagement with to ground, each relay havinga make contact normally a fixed front contact 34. positioned out ofengagement with a front contact, said The rectifier 21 is connected to arelay 35 having a make contacts being connected together, one of said:011 37 grounded at 38. The relay 35 is similar to the front contactsbeing connected in circuit with the center 'elay 22 in that it isadapted to actuate a transfer contact wire of the system and includingan indicator, the front contact of said other relay being connected incircuit with one outside wire of the system, each relay also having atransfer contact normally positioned in engageand being movable intoengagement with a fixed front contact, said transfer contacts beingconnected together, said back contacts engaged by said transfer contactsbeing connected together and to'said one outside wire of the system, andeach of said front contactsrengageable by said transfer contacts beingconnected to cluding an indicator.

the center wire of the system and in- 10 References Cited in the file ofthis patent I Number Number UNITED STATES PATENTS Nam Date Cook Dec. 11,1945 Fountain Oct. 7, 1947 FOREIGN PATENTS Country Dat e Great BritainApr. 30, 1928

